1. Field of the Invention
The present invention relates generally to a color separation optical system, and more particularly to a color separation optical system which is suitable for a compact color scanner which uses a 3-line CCD.
2. Description of Related Art
A hand-scanner captures image information of a subject (e.g. a piece of paper, a picture, etc.), while moving along the subject, by illuminating the subject with an illumination light source and guiding light which is reflected by the subject and which enters the hand-scanner through a read opening (a slit) to a line sensor consisting of charge coupled devices (CCD) via a lens. In order to secure a conjugate distance of the lens, a plurality of mirrors for turning and lengthening an optical path are arranged in a casing of the conventional scanner.
In a color hand-scanner, which captures color image of a color subject, two dichroic mirrors are provided to separate incident light into rays of the three primary colors, red (R), green (G) and blue (B), and the CCD of each color channel receives the rays of each color. A first dichroic mirror which reflects blue light separates the blue light from the incident light, and the light which is transmitted through the first dichroic mirror meets a second dichroic mirror which reflects green light. The second dichroic mirror separates the green light from the falling light, and red light is transmitted through the second dichroic mirror. Thus, the incident light is separated into the blue light, the green light and the red light.
In the above-mentioned conventional scanner optical system, however, it is necessary to finely adjust arrangement angles of the mirrors which are arranged to secure the conjugate distance, and it is extremely difficult to arrange the plurality of mirrors at proper arrangement angles. If the number of turns of the optical path increases, the number of mirrors must also be increased, so that the scanner optical system cannot be compact.
In particular, in the case of the color scanner which uses a 3-line CCD, rays of the three colors must be separated from one another at proper intervals in accordance with arrangement of light receiving channels of the colors in the CCD.